Conventionally, a system is widely prevalent in which a vehicle door is remotely locked or unlocked by wireless communication performed between a vehicle-mounted communication device that is provided in the vehicle and a portable communication device in a user's possession. This system can be called a keyless entry system or a smart entry system. Such a system is sometimes provided with a mechanical key for locking or unlocking the vehicle door in the case where a malfunction, battery exhaustion, or the like occurs in the portable communication device in the user's possession.
JP 2009-177644A discloses a mobile device that has a transmission/reception circuit for transmitting and receiving wireless signals via an antenna, and also has an emergency mechanical key that is retrievably stored in a storing portion. The mobile device disclosed in JP 2009-177644A includes a push switch that detects whether or not the mechanical key is stored in the storing portion, and a control device that performs wireless signal directivity correction by controlling an antenna switching switch according to whether or not the mechanical key is stored. Also, JP 2009-177642A discloses a similarly-configured mobile device that includes an impedance matching circuit that adjusts the impedance between an antenna and a transmission/reception circuit, and a control device that controls the impedance matching circuit according to whether or not the mechanical key is stored.
Portable communication devices for locking and unlocking a vehicle door are carried by users, and therefore there is desire for size reduction. The smaller the portable communication device is, the greater the need is to also reduce the size of the antenna for performing wireless signal transmission and reception, and there is a problem of degradation in communication efficiency. The mobile devices disclosed in JP 2009-177644A and JP 2009-177642A are for preventing a reduction in communication efficiency caused by the presence of the mechanical key, and therefore fundamentally cannot solve this problem.
The present invention was achieved in light of the foregoing situation, and an object of the present invention is to provide a portable communication device that can suppress degradation in communication efficiency caused by a reduction in device size.